Why sometimes CI4 crashes after a composer update?

Looks like you are missing some of the error view files. However, we should have a better fallback in place for this. There is no “else” for if the files aren’t found :

PHP Code:

        // Check if the view exists
        if (is_file($path . $view))
        {
            $viewFile = $path . $view;
        }
        elseif (is_file($altPath . $altView))
        {
            $viewFile = $altPath . $altView;
        } 


I think this would be an easy fix. Would you submit a bugfix on GutHub? In the meantime, look in your app/Views/errors folders and make sure you have all the same files that are in the repo/download.